Update imports from hoppr for 1.8.0

Several module paths have changed in the upcoming hoppr version 1.8.0. Plugin project imports need to be updated to align (one time only). For example, these:

from hoppr.base_plugins.hoppr import hoppr_rerunner
from hoppr.context import Context
from hoppr.result import Result

become:

from hoppr import HopprContext, Result, hoppr_rerunner

across the plugin project.

Additional updates required in order to align with Hoppr 1.8.0 release:

• Refactor to work with changes from hoppr/hoppr!308 (merged)